The shoulder joint is kind of unique in that there are no ligaments to hold it in place. That wold limit the range of motion. Instead, the humerus (uper arm bone) is held in the socket by a number of muscles pulling from varius directions. Exercises to strengthen those muscles might help limit the dislocations. You would probably need to talk to a good physiotherapist or orthopedist to determine which muscles, in particular, need strengthened and what exercises should be used to strengthen them. If that seems to them a good idea, you should start out slowly, with only a few repetitions and little or no added weight, then build into a more rigorous program gradually, lest you injure yourself.